Simultaneous anti-jamming forward-looking imaging method for missile-borne forward-looking array radar

Abstract

The application discloses a method for simultaneously resisting suppressing interference forward-looking imaging of a missile-borne forward-looking array radar, adopts an array antenna in a cut-off track direction to receive echoes of a forward-looking area, and samples to obtain distance-pulse-array three-dimensional echo data; pulse compression in the distance direction is performed on the three-dimensional echo data, a pulse compression reference function and a migration correction factor are multiplied in the frequency domain, and high resolution in the distance direction is realized; multi-channel receiving data of each distance-pulse unit is selected, and is sequentially arranged to form a corresponding space snapshot of the unit; a covariance matrix of interference and noise is established, and the maximum likelihood estimation value of the target angle and amplitude in the interference environment is approximately solved by using an adaptive single-pulse algorithm on the space snapshot signal of each distance-pulse unit after distance pulse compression; and the angle measurement result is projected to the distance-azimuth domain, and through space coordinate conversion, a two-dimensional forward-looking imaging diagram is obtained. The application realizes high-resolution imaging of a forward-looking target while effectively suppressing main lobe suppressing interference.

Description

[0001] Method Domain

[0002] This invention belongs to the field of radar imaging technology, and relates to airborne radar forward-looking imaging signal processing technology, specifically to a forward-looking imaging method for missile-borne forward-looking array radar that simultaneously resists suppression and interference. Background Technology

[0003] Radar imaging technology is a significant milestone in the history of radar development. Through advanced signal processing, it can acquire high-resolution two-dimensional images of the detection area, greatly expanding the capabilities of modern radar systems. Mathematically, radar imaging is essentially a typical inverse problem: retrieving a high-resolution ground scene from limited observation data (echo signals). Through high-resolution imaging processing, missile-borne radar systems can acquire topographical features, sea surface characteristics, and the size and shape of targets within the strike area, thereby improving strike accuracy and combat efficiency. However, in the terminal guidance phase of existing precision-guided weapons, especially within 5 kilometers of the target, radar systems cannot use Synthetic Aperture Radar (SAR) mode to acquire high-resolution images of forward-looking targets and can only lock onto targets using single-pulse tracking. Furthermore, when the target is in formation, or when false targets or interference exist, this operating mode often fails to meet the requirements of precision guidance. When missiles are in a three-dimensional accelerated forward-looking operating mode during the terminal guidance phase, high-resolution imaging of the moving forward-looking strike area is one of the essential functions of modern missile-borne radar systems.

[0004] Compared to traditional single-channel radar, array radar super-resolution imaging technology, based on an array receiving system, utilizes super-resolution algorithms to achieve high-resolution forward-looking imaging for airborne radar. This technology can achieve angular resolution far exceeding the actual aperture beamwidth, separating multiple targets within the beam. In recent years, as a new technical means for forward-looking imaging of airborne radar, super-resolution technology has gradually been recognized and valued by relevant research institutions, and is one of the simple and efficient methods to solve the challenges of forward-looking imaging for airborne radar in the future.

[0005] However, with the increasing complexity of the electromagnetic environment, main lobe suppression interference can severely degrade the performance of existing forward-looking imaging algorithms, affecting the strike effect of attack weapons. How to image the forward-looking area of ​​missile-borne radar under such interference scenarios is an urgent problem to be solved in the field of forward-looking imaging. Summary of the Invention

[0006] Purpose of the invention: This invention provides a forward-looking imaging method for missile-borne forward-looking array radar that simultaneously resists suppression interference, enabling the radar to achieve high-resolution imaging of forward-looking targets while effectively suppressing main lobe suppression interference.

[0007] Technical solution: The present invention provides a method for simultaneous anti-suppression jamming forward-looking imaging for missile-borne forward-looking array radar, comprising the following steps:

[0008] (1) The missile-borne radar works in a scanning mode, and a cut-track direction array antenna is used to receive echoes in a forward-looking region to obtain distance-pulse-array three-dimensional echo data by sampling;

[0009] (2) Pulse compression is performed on the array radar three-dimensional echo data in the distance direction, and a pulse compression reference function and a migration correction factor are multiplied in the frequency domain to realize high resolution in the distance direction;

[0010] (3) Multi-channel received data of each distance-pulse unit is selected to form a corresponding spatial snapshot of the unit in sequence;

[0011] (4) A covariance matrix of main lobe interference and noise under the missile-borne forward-looking condition is established, and a range-pulse compressed data is processed in the azimuth direction by distance gate imaging, a corresponding spatial snapshot signal of each distance-pulse unit is constructed, a maximum likelihood function is established, and then a maximum likelihood target estimation value of target angle and amplitude under the interference environment is solved by using an adaptive single pulse algorithm;

[0012] (5) The spatial snapshot of each distance-pulse unit in the echo data is projected into a two-dimensional preset grid in the distance-azimuth domain through the target estimation value, and a two-dimensional forward-looking imaging map is obtained through spatial coordinate conversion.

[0013] Further, the step (1) is implemented as follows:

[0014] A horizontal array antenna along the cut-track direction is used to receive missile-borne radar forward-looking region echoes through subarray synthesis of multiple receiving channels; the radar works in a scanning mode, and a linear frequency modulation pulse (LFM) is transmitted every pulse repetition interval (PRI), and the beam scans a circle, and then the echo is sampled to obtain distance-pulse-channel three-dimensional echo data of the missile-borne radar forward-looking region.

[0015] Further, the sampling of the distance-pulse-array three-dimensional echo data in step (1) is implemented as follows:

[0016] The specific form of the echo obtained by the whole imaging scanning process about a single point target after one circle of beam scanning is as follows:

[0017]

[0018] Wherein, h(t-t p ) represents a two-way antenna pattern in the azimuth direction, which changes with the slow time variable t and represents the modulation effect in the azimuth direction, t p represents the time when the beam center of the antenna scans the point target P; τ0(t) is the propagation delay of the transmitted signal reflected by the target P to the mth channel, d mwhere d m is the distance between the mth receiving channel and the reference element, then the time delay τ 0 (t) is:

[0019]

[0020] where c is the speed of light; after the down-conversion, the 2D range-doppler echo of the mth receiving channel is:

[0021]

[0022] The echo is sampled to obtain the 3D range-pulse-channel echo data of the forward-looking area of the missile-borne radar.

[0023] Further, the step (2) is implemented as follows:

[0024] After the range FFT of the echo of each channel after the down-conversion, the following is obtained:

[0025]

[0026] where B is the signal bandwidth, f r is the range frequency domain variable; in the frequency domain, the following pulse compression reference function is multiplied:

[0027]

[0028] The following is obtained:

[0029]

[0030] The echo is range-migrated, and the following phase factor is multiplied in the range frequency domain to eliminate the influence of platform motion:

[0031]

[0032] After the pulse compression and migration correction in the range direction, high-resolution imaging in the range direction is implemented.

[0033] Further, the step (3) is implemented as follows:

[0034] The entire imaging area is divided into L range units and K azimuth angle units; for a certain range unit, the Kx1-dimensional source signal vector composed of the backscattering coefficients of the scattering points in the range unit is represented as x=[σ 1, …, σ K ]. K ] T σ k represents the backscattering coefficient of the kth scattering point, k=1, 2, …, K; at a certain moment, the beam center is directed to the azimuth angle θ k The sampling of all channel echoes, i.e., a certain spatial snapshot, is represented as s=[s 1, s 2, …, s L ]. M s l represents the echo of the lth channel, l=1, 2, …, L; the spatial snapshot is transformed into the range-doppler domain to obtain the following:M ]; by θ k Mx1 dimensional spatial steering vector a consisting of phase difference of target reaching horizontal linear array s (θ k ) is expressed as:

[0035]

[0036] where M is the number of channels, d is the channel spacing, λ is the wavelength, is the radar beam downward angle;

[0037] The spatial snapshot is expressed in the following matrix form:

[0038] s = Ax + N

[0039] where A is the MxK dimensional spatial steering vector matrix, N is the Mx1 dimensional observation noise vector, and are expressed as:

[0040]

[0041] N = [n1, …, n M ] T .

[0042] Further, the step (4) is implemented as follows:

[0043] The statistical characteristics of the interference superimposed noise are used to establish the covariance matrix R of the interference and noise, and the spatial snapshot data of each range-pulse unit is selected for azimuth imaging processing; the maximum likelihood function P(θ) = |w H s| 2 is constructed, where w = (a s H R -1 a s ) -1 / 2 R -1 a s is the adaptive and beam weight vector, s is the spatial snapshot signal, and the θ value that maximizes P(θ) is the maximum likelihood estimate

[0044] The likelihood function is approximately solved, let F(θ) = ln[P(θ)], and the estimated value of the expected target is The solution of the log-likelihood function F(θ) is given by the Newton gradient method:

[0045] θ max = θ0-F θθ -1 (θ max )F θ (θ)

[0046] where Fθ (θ) is the first derivative of F(θ), F θθ (θ) is the second derivative of F(θ), θ0 is the beam center of the current range-pulse unit antenna pattern azimuth direction; the first derivative and the second derivative of F(θ) are calculated and substituted into the above formula to obtain:

[0047]

[0048] Wherein:

[0049]

[0050] The angle and amplitude information of the real target under the main lobe interference condition are obtained through the above formula, and in the case that external interference exists, the correction coefficient in the adaptive single pulse algorithm compensates the error, so that the correct direction of arrival estimation result is obtained.

[0051] Further, the step (4) is implemented as follows:

[0052] The target estimation value corresponding to each range-pulse unit is projected into a preset grid matrix in the range-azimuth domain according to the range gate, the current beam center and the azimuth angle, and the stored data after projection is subjected to spatial coordinate conversion and display to obtain the forward-looking area imaging result.

[0053] Beneficial effects: Compared with the prior art, the beneficial effects of the present application are: the present application considers the inevitable noise suppression type interference in the forward-looking imaging of the missile-borne radar, utilizes the statistical characteristics of the interference and noise, establishes the likelihood function and solves to obtain the maximum likelihood estimation value of the target amplitude on the basis of establishing the interference and noise covariance matrix, and combines the Newton formula to complete the angle estimation through the adaptive single pulse, avoids the traversal search on all possible azimuths, and reduces the operation amount; the present method is based on the missile-borne array radar, can obtain good angle measurement precision while effectively suppressing the main lobe suppression type interference, and realizes the high-resolution imaging of the forward-looking target. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 is the flowchart of the present application;

[0055] Figure 2 is the schematic diagram of the forward-looking imaging geometry model of the missile-borne array radar;

[0056] Figure 3 is the schematic diagram of the simplified two-dimensional data acquisition;

[0057] Figure 4 is the schematic diagram of the spectrum non-coherent accumulation;

[0058] Figure 5 is the schematic diagram of the point target simulation scene;

[0059] Figure 6 The imaging result of the point target by the real beam;

[0060] Figure 7 The imaging result of the point target by the forward-looking imaging while resisting the jamming;

[0061] Figure 8 The profile of the imaging result of the point target by the forward-looking imaging while resisting the jamming;

[0062] Figure 9 The schematic diagram of the ship model composed of the point array;

[0063] Figure 10 The imaging result of the signal-to-interference ratio of-20dB by the maximum likelihood estimation algorithm; wherein, (a) is the imaging result of the real beam, and (b) is the imaging result of the forward-looking imaging while resisting the jamming;

[0064] Figure 11 The imaging result of the signal-to-interference ratio of-10dB by the maximum likelihood estimation algorithm; wherein, (a) is the imaging result of the real beam, and (b) is the imaging result of the forward-looking imaging while resisting the jamming;

[0065] Figure 12 The imaging result of the signal-to-interference ratio of-5dB by the maximum likelihood estimation algorithm; wherein, (a) is the imaging result of the real beam, and (b) is the imaging result of the forward-looking imaging while resisting the jamming;

[0066] Figure 13 The imaging result of the signal-to-interference ratio of 0dB by the maximum likelihood estimation algorithm; wherein, (a) is the imaging result of the real beam, and (b) is the imaging result of the forward-looking imaging while resisting the jamming;

[0067] Figure 14 The imaging result of the signal-to-interference ratio of 5dB by the maximum likelihood estimation algorithm; wherein, (a) is the imaging result of the real beam, and (b) is the imaging result of the forward-looking imaging while resisting the jamming;

[0068] Figure 15 The imaging result of the signal-to-interference ratio of 10dB by the maximum likelihood estimation algorithm; wherein, (a) is the imaging result of the real beam, and (b) is the imaging result of the forward-looking imaging while resisting the jamming. DETAILED DESCRIPTION

[0069] The application will be further described in detail below with reference to the accompanying drawings.

[0070] As shown in the drawings, the application provides a forward-looking imaging method for resisting jamming simultaneously for a missile-borne forward-looking array radar, which specifically comprises the following steps: Figure 1

[0071] ​Step 1: The missile-borne radar works in scanning mode, and uses the array antenna along the cross-track direction to receive the echo of the forward-looking area. The three-dimensional echo data of range-pulse-array are sampled.

[0072] As shown in Figure 2 , the missile-borne radar uses the horizontal array antenna along the cross-track direction to receive the echo of the forward-looking area through the synthesis of M receiving channels. The forward-looking area generally considers the area of ±10° in the direction of the missile flight. The radar works in the downward scanning mode, and transmits a linear frequency modulation (LFM) pulse every pulse repetition interval (PRI). The time-domain expression is:

[0073]

[0074] Where τ is the fast time-domain variable in the range direction, f c is the carrier frequency of the radar transmitted signal, K r is the linear frequency in the range direction, T p is the pulse width of the signal, and rect[·] represents the rectangular window function, i.e.:

[0075]

[0076] Assume that t is the slow time-domain variable in the azimuth direction, which is related to the radar movement and antenna scanning. For a point target P in the imaging area, assume that the position coordinates of the target P at t=0 are (R0, θ0), and the scattering coefficient is σ0, is the downward angle of the radar beam, which is a constant. At any t time, the instantaneous slant range R(t) between the reference element of the radar array antenna and the target P is approximately expressed as:

[0077]

[0078] Where v is the movement speed of the missile-borne radar. For the mth receiving channel of the multi-channel radar, m=1, 2, …, M, the specific form of the echo obtained by the radar after scanning a circle is:

[0079]

[0080] Where h(t-t p ) represents the two-way antenna pattern in the azimuth direction, which changes with the slow time variable t and represents the modulation effect in the azimuth direction. t p represents the time when the beam center of the antenna scans to the point target P; τ0(t) is the propagation time delay of the transmitted signal reaching the target P and then being reflected to the mth channel by the target P; d m represents the distance between the mth receiving channel and the reference element, so the time delay τ0(t) is:

[0081]

[0082] where c is the speed of light.

[0083] After the down-conversion processing, the range-azimuth two-dimensional echo of the mth receiving channel is expressed as:

[0084]

[0085] Sampling the echo can obtain the range-pulse-channel three-dimensional echo data of the missile-borne radar forward-looking area.

[0086] Step 2: Pulse compression and migration correction in the range direction of the array radar three-dimensional echo data to realize high resolution in the range direction.

[0087] Pulse compression and migration correction in the range direction of the array radar three-dimensional echo data, multiplying the pulse compression reference function and the migration correction factor in the frequency domain to realize high resolution in the range direction. Then, the multi-channel receiving data of each range-pulse unit is selected and arranged in sequence to form the corresponding spatial snapshot of the unit.

[0088] After the range direction FFT of the echo of each channel after the down-conversion, the following is obtained:

[0089]

[0090] where B is the signal bandwidth, f r is the range direction frequency domain variable. Multiply the following pulse compression reference function in the frequency domain:

[0091]

[0092]

[0093]

[0094] The missile-borne radar has a high-speed motion and a distance migration with the target, which causes the coupling of the range and azimuth directions while bringing the Doppler shift. In order to decouple, the echo needs to be corrected for distance migration. Therefore, the following phase factor is multiplied in the range frequency domain to eliminate the influence of platform motion:

[0095]

[0096] After pulse compression and migration correction in the range direction, high resolution imaging in the range direction has been realized.

[0097] Step 3: In order to realize high resolution imaging in the azimuth direction, a multi-channel signal echo model is constructed.

[0098] ​First, the forward-looking area is divided into an azimuth grid. Assume the entire imaging area is divided into L range cells and K azimuth angle cells. The slant range of the target in the l-th range cell and the k-th azimuth angle cell are respectively represented by R... l and θ k It represents the scattering coefficient σ(R) l ,θ k This indicates that, for a given range cell, the azimuth angle θ is the angle at which the beam center points to the azimuth at a specific moment. k At that time, the K×1 dimensional source signal vector composed of the backscattering coefficients of the scattering point of the range cell can be expressed as x=[σ1,…,σ K ] T The sampling of echoes from all channels, i.e., a spatial snapshot, is represented as s = [s1, s2, ..., s]. M ]. By θ k The M×1 spatial guidance vector a is composed of the phase difference between the target and the horizontal linear array. s (θ k ) is represented as:

[0099]

[0100] Where d is the channel spacing and λ is the wavelength.

[0101] Therefore, this spatial snapshot can be represented in the following matrix form:

[0102] s = Ax + N

[0103] Where A is an M×K dimensional spatial guidance vector matrix, and N is an M×1 dimensional observation noise vector, respectively represented as:

[0104]

[0105] N = [n1, ..., n] M ] T .

[0106] Step 4: Establish the covariance matrix of main lobe interference and noise under missile-borne forward-looking conditions, perform azimuth imaging processing on the range pulse compressed data by range gate, construct the corresponding spatial snapshot signal for each range-pulse unit, establish the maximum likelihood function, and then use the adaptive single-pulse algorithm to solve the maximum likelihood estimate of the target angle and amplitude under interference conditions.

[0107] Maximum likelihood estimation obtains the estimated value of the angle of arrival by establishing the following likelihood function and solving it:

[0108]

[0109] Its exponential part is denoted as:

[0110] U(σ, θ) = (s - σa s ) H R -1 (s - σa s )

[0111] The maximum likelihood estimate of σ can be obtained by taking the partial derivative of U(σ, θ) with respect to σ and setting it equal to zero:

[0112]

[0113] Substituting this into U(σ, θ) gives:

[0114] U(σ, θ) = s H R -1 s+|w H s| 2

[0115] Define the adaptive and beam weight vectors as:

[0116] w = (a s H R -1 a s ) -1 / 2 R -1 a s

[0117] Let P(θ) = |w H s| 2 Since the previous term is a constant term independent of θ, the value of θ that maximizes P(θ) is the maximum likelihood estimate of θ Since There is no analytical expression, so in practical processing, all possible orientations need to be searched to find the orientation position that maximizes P(θ). Next, the likelihood function is solved by the adaptive monopulse algorithm, let F(θ) = ln[P(θ)], then the estimated value of the expected target is The solution of the log-likelihood function F(θ) is given by the Newton gradient method:

[0118] θ max = θ0 - F θθ -1 (θ max )F θ (θ)

[0119] In the formula, F θ (θ) is the first derivative of F(θ), F θθ (θ) is the second derivative of F(θ), and θ0 is the current distance-pulse unit antenna pattern orientation beam center. The first and second derivatives of F(θ) are calculated and substituted into the above formula to obtain:

[0120]

[0121] wherein:

[0122]

[0123] The angle and amplitude information of the real target under the main lobe interference condition can be obtained by the above formula. In the presence of external interference, the correction coefficient in the adaptive monopulse algorithm compensates for the error, thereby obtaining the correct direction of arrival estimation result.

[0124] Step 5: Project each distance-pulse unit space snapshot in the echo data into the distance-azimuth domain two-dimensional preset grid by the target estimation value obtained in step 4, and obtain the two-dimensional forward-looking imaging map through spatial coordinate conversion.

[0125] Project the target estimation value corresponding to each distance-pulse unit obtained in step 4 into the preset grid matrix in the distance-azimuth domain according to the distance gate, the current beam center and the azimuth angle, and the forward-looking area imaging result can be obtained by spatial coordinate conversion and display of the stored data after projection, as shown in Figure 3 and Figure 4 .

[0126] Point target simulation and ship surface target simulation verification are performed as follows. Figure 5 The point target simulation scene is shown in FIG. 1, and a point target and a suppressing interference are set within the main lobe width of the beam. The interference is located in front of the missile flight trajectory, and the target deviates from the interference by 1 degree. Figure 6 and Figure 7 The processing results of the point target forward-looking simulation echo data under the main lobe interference scene are shown in FIGS. 2 and 3, respectively. The real beam imaging result of the forward-looking scene is shown in FIG. 4. In the presence of main lobe interference, the target cannot be imaged, which seriously affects the precision strike performance of the missile. Then, the array adaptive maximum likelihood estimation method is used to image the forward-looking area, and the result is shown in FIG. 5. When the array is suppressed by noise, this method accurately estimates the direction of arrival and amplitude of the target by using the maximum likelihood method, and suppresses the noise. For easy comparison, the profile graphs of the real beam imaging and the adaptive monopulse imaging are shown in FIG. 6. It can be seen that the proposed new missile-borne array radar forward-looking imaging algorithm has the ability to resist the suppressing interference in the strike area at the end of guidance, and enables the radar to have the ability to image the forward-looking area in the presence of suppressing interference. Figure 6 Figure 7 Figure 8

[0127] Next, ship surface target simulation verification is performed, Figure 9 the ship model is composed of point arrays; Figures 10 to 15 ​​​The processing results of the forward-looking simulation echo data of the ship model under different signal-to-interference ratios are given by using the maximum likelihood estimation algorithm, the angle estimation of the target in the interference background is realized, and finally the forward-looking image after the noise suppression jamming is obtained by the non-coherent accumulation of the target estimation value, and the ship contour is clearly visible.

[0128] The embodiments of the present application are described above with reference to the drawings; however, the present application is not limited to the specific embodiments described above, and the specific embodiments described above are merely illustrative rather than restrictive, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, and these all belong to the protection of the present application.

Claims

1. A method for simultaneous anti-jamming forward-looking imaging for a missile-borne forward-looking array radar, characterized in that, The method comprises the following steps: (1) The missile-borne radar works in a scanning mode, and a cut-track direction array antenna is used to receive echoes in a forward-looking area, and sampling is performed to obtain distance-pulse-array three-dimensional echo data; (2) Pulse compression is performed on the array radar three-dimensional echo data in the distance direction, a pulse compression reference function and a shift correction factor are multiplied in the frequency domain, and high resolution in the distance direction is realized; (3) Multi-channel received data of each distance-pulse unit is selected, and space snapshots corresponding to the unit are sequentially arranged; (4) A covariance matrix of main lobe interference and noise under the missile-borne forward-looking condition is established, imaging processing in the azimuth direction is performed on the distance pulse compressed data in each distance gate, a space snapshot signal corresponding to each distance-pulse unit is constructed, a maximum likelihood function is established, and then a maximum likelihood target estimation value of the target angle and amplitude in the interference environment is solved by using an adaptive single pulse algorithm; (5) The space snapshot of each distance-pulse unit in the echo data is projected into a distance-azimuth domain two-dimensional preset grid through the target estimation value, and a two-dimensional forward-looking imaging diagram is obtained through space coordinate conversion. The step (4) is implemented in the following manner: The statistical characteristics of the interference superimposed noise are used to establish a covariance matrix R of the interference and noise, and then the space snapshot data of each distance-pulse unit is selected for imaging processing in the azimuth direction. Construct the maximum likelihood function P(θ) = |w H s 2 where w = (a s H R -1 a s ) -1 / 2 R -1 a s is the adaptive and beam weight vector, s is the spatially snapped signal, and the value of θ that maximizes P(θ) is the maximum likelihood estimate The approximate solution of the likelihood function is given by F(θ) = ln[P(θ)], and the estimate of the expected target is The solution of the log-likelihood function F(θ) is given by the Newton gradient method: θ max = θ0- F θθ -1 (θ max )F θ (θ) where F(θ) is the current distance-pulse cell antenna pattern, θ0is the beam center of the current distance-pulse cell antenna pattern azimuth, and θ is the azimuth of the target. θ (θ) is the first derivative of F(θ), F θθ (θ) is the second derivative of F(θ), and θ0is the beam center of the current distance-pulse cell antenna pattern azimuth. The first derivative and the second derivative of F(θ) are calculated and substituted into the above equation to obtain: In the step (1), the following implementation process is adopted: where a s is the spatial steering vector, the angle and amplitude information of the real target under the main lobe interference condition is obtained by the above formula, and the correction coefficient in the adaptive monopulse algorithm compensates the error in the presence of external interference, so as to obtain the correct direction of arrival estimation result.

2. The method of claim 1, wherein, A horizontal array antenna along the cut-track direction is used to receive the missile-borne radar forward-looking area echoes through subarray synthesis of multiple receiving channels; the radar works in a scanning mode, a linear frequency modulation pulse (LFM) is transmitted every pulse repetition interval (PRI), and the echoes are sampled after one round of beam scanning to obtain the distance-pulse-channel three-dimensional echo data of the missile-borne radar forward-looking area. The sampling of the distance-pulse-array three-dimensional echo data in the step (1) is implemented in the following manner:

3. The method of claim 1, wherein, The specific form of the echoes obtained about a single point target in the whole imaging scanning process after one round of beam scanning is as follows: The echoes are sampled to obtain the distance-pulse-channel three-dimensional echo data of the missile-borne radar forward-looking area. where σ0is the scattering coefficient, rect[·] represents the rectangular window function, τ is the distance fast-time domain variable, f c is the carrier frequency of the radar transmitted signal, K r is the linear frequency modulation in the range direction, h(t-t p ) represents the two-way antenna pattern in the azimuth direction, which varies with the slow-time variable t, t p represents the time when the beam center of the antenna sweeps to the point target P; τ0(t) is the propagation delay from the transmitted signal to the target P and then reflected to the mth channel by the target P, d m represents the distance between the mth receiving channel and the reference array element, so the time delay τ0(t) is: where R(t) is the instantaneous slant range between the radar array antenna reference element and the target P, θ0is the azimuth angle of the target, is the down-view angle of the radar beam, and c is the speed of light; after the down-conversion processing, the range-azimuth two-dimensional echo of the mth receiving channel is expressed as The step (2) is implemented in the following manner:

4. The method of claim 3, wherein, After the distance direction FFT of the echoes of each channel after frequency down conversion, the following is obtained: The following is obtained: where B is the signal bandwidth, f r is the range-to-frequency variable; multiply in the frequency domain by the following pulse compression reference function: The echoes are subjected to distance shift correction, and the following phase factor is multiplied in the distance frequency domain to eliminate the influence of platform motion: After pulse compression and shift correction in the distance direction, high resolution imaging in the distance direction is realized. The step (3) is implemented in the following manner:

5. The method of claim 4, wherein, The space snapshot is expressed in the following matrix form: The whole imaging region is divided into L distance units and K azimuth angle units; for a certain distance unit, the K*1 dimensional source signal vector composed of the backscattering coefficients of the scattering points in the distance unit is represented as x = [σ1,..., σK]T. K ] T , σ k k = 1, 2,..., K represents the backscattering coefficient of the kth scattering point. At a specific moment, the beam center points to the azimuth angle θ. k At that time, the sampling of echoes from all channels, i.e., a certain spatial snapshot, is represented as s = [s1, s2, ..., s]. M ]; by θ k The M×1 spatial guidance vector a is composed of the phase difference between the target and the horizontal linear array. s (θ k ) is represented as: where M is the number of channels, d is the channel spacing, and λ is the wavelength, is the radar beam depression angle; s = Ax + N Wherein, A is an M*K dimensional space steering vector matrix, and N is an M*1 dimensional observation noise vector, which are respectively expressed as: The step (4) is implemented in the following manner: N = [n1,..., n M ] T .

6. The method of claim 1, wherein, The target estimation value corresponding to each distance-pulse unit is projected into a distance-azimuth domain preset grid matrix according to the distance gate, the current beam center and the azimuth angle, the stored data after projection is subjected to space coordinate conversion and display, and the forward-looking area imaging result is obtained. ​

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